A romantic stargazer who was just days away from whisking away his girlfriend on a surprise Paris trip to pop the question plummeted to his death early yesterday morning when he fell from the roof of his Massachusetts Avenue apartment. “He had the tickets. He had the ring. He just didn’t have the time,” said Don Coulon, whose 28-year-old son, Gregory, was found dead after falling from the roof at 552 Massachusetts Ave. Coulon, 28, a Boston University systems analyst and computer programmer, was set to jet his girlfriend of several years, Michelle Kovach, to the City of Lights Wednesday...